Conveying devices, such as those which are used for moving objects between different stations in a factory, usually comprise a conveying track in the form of a belt or a chain. The conveying tracks can be recessed in a trench with vertical side surfaces. Alternatively, they can be located on the horizontal upper surfaces of the trench or arranged in some other way. The objects to be conveyed are arranged slidably in relation to the conveying tracks, either directly or via supporting means. Larger objects are often conveyed on supporting means also known as pallets, and smaller objects may be conveyed using a small carrier often referred to as a carrier puck. Many objects are conveyed directly by the conveyor chain.
The conveyor chain is forwarded by a drive unit comprising a motor. The conveyor chins runs in conveyor beams and glides on slide rails attached to the conveyor beams. Both the conveyor chain and the slide rails may be made from a low friction material in order to reduce power consumption, to reduce wear and to reduce noise caused by vibrations. In the forward direction, i.e. when the chain transports objects, the underside of the upper body bears on upper slide rails of the conveyor beam. In the return direction, i.e. when the chain travels upside down in the return path, the upper side of the conveyor chain may be supported by a bearing surface on which the conveyor chain glides. The conveyor chain may also be provided with tabs or protrusions by which the chain may bear on an inner slide rail of the conveyor beam.
One problem with a sliding contact between the conveyor chain and the conveyor beams is that friction is created. One way of reducing friction is to use a low friction material in the chain links and in the slide rails. It is however not always possible to select a low friction material for the conveyor chain. For some types of transportation, it is required that the conveyor chain is ESD proof, i.e. that the conveyor chain is not charged with static electricity. In this case, the material of the conveyor chain must contain particles that allow the conveyor chain to conduct electricity. Such a material has a reduced wear resistance and a higher friction value.
In other cases, a high friction material may be required on the carrying surface of the conveyor chain. In some environments, it is of advantage to provide the conveyor chain top in a metal or metal compound material. It is however complicated to manufacture the complete chain link in metal.
It would thus be of advantage to use chain links comprising different materials with different properties.
In EP 1 975 093 A1, a chain comprising inner and outer links (2, 3) is described. The inner and outer links comprise separate upper plates attached to the inner and outer links by resilient catches which are inserted into receiving slots in the inner and outer links.
U.S. Pat. No. 6,347,699 B1 describes a two piece pivot chain link which through its construction allows the top platform piece to be removably replaceable. The top platform is provided with resilient snap tabs adapted to be inserted into a main body orifice. The top platform is removed by pressing one of the snap tabs.
DE 102 07 687 A1 describes a transport chain having chain links comprising lower guide pieces and upper support pieces. A support piece is provided with resilient catches which are inserted into an opening of the guide piece having protruding noses for attaching the support piece to the guide piece. A locking member can be inserted between the catches to lock the upper piece in place.
GB 1537876 A describes a conveyor chain having overlapping slats forming an upper surface of the conveyor chain. The slats are attached to the slat carriers by resilient pawls which engage cavities in the slat carrier. The slats can be easily removed and replaced.
In the above solutions, the upper portion of the chain link is attached to the lower portion by means of resilient catches. The resilient catches may be pressed on such that the catch moves away from the catching surface in order to remove the upper portion. With such a solution, there is a risk that the catches disengage unintentionally, e.g. when the conveyor system has a malfunction or when an excessive force is applied to the conveyor chain link.
U.S. Pat. No. 6,347,699 B1 describes a conveyor chain comprising a main body and a top platform piece, where the top platform piece can be easily removed and replaced.
CA 1,217,162 describes a conveyor chain comprising removable top slats that can be easily replaced. The lower connecting member is attached to a chain. The removal of the top slat allows the connection member to be attached to the chain.
These solutions work fine in some systems, but there are still room for improvements.